1. Field of the Invention
The invention relates to an improved apparatus for hydraulically forming pulleys from cup-shaped sheet metal blanks in a continuous forming operation. More particularly, the invention relates to an apparatus having mechanically locking means for locking a pair of half-die holding members and groove-forming dies in both the horizontal and vertical directions in a closed position about a cup blank and formed pulley, preventing the formation of die marks on the hydraulically formed pulley product.
2. Description of the Prior Art
Numerous apparatus and procedures have been proposed for forming sheet metal pulleys from a cup-shaped blank by hydraulically bulging the cup walls during the axial compression of the cup-shaped blank to force the metal of the cup wall outwardly into forming grooves of the surrounding dies. Some examples of such apparatus and methods which have been proposed and used are shown in U.S. Pat. Nos. 2,493,053, 2,743,691, 2,929,345, 3,124,090, 3,335,590, 3,630,056, and 3,820,369. The present invention is a particular improvement on the apparatus shown in U.S. Pat. Nos. 3,837,200 and 3,935,627.
Known apparatus such as disclosed in these patents have proven somewhat satisfactory in forming the final pulley product. However, a particular problem which has developed during the hydraulic bulge forming of a pulley with known equipment is the creation of die junction marks on the formed pulley. These die marks require an additional machining or metal spinning procedure to remove the marks. Considerable hydraulic pressure is exerted outwardly against the metal of the cup wall in order to force the metal into the die forming grooves. Consequently, this metal is forced outwardly into the junction areas of the mated die sections. Even though these joints are relatively small and only a small amount of metal is forced therein, it results in an imperfection or ridge on the produced pulley, which must be removed by an additional manufacturing operation. Even though the dies are clamped in a closed position in most prior apparatus, the exerted hydraulic pressure still forces the dies apart a sufficient distance to create die marks on the formed pulley.
This problem becomes increasingly acute when a burst of an extremely high pressure is exerted in the hydraulic bulging fluid to impart a final set to the metal, such as generated by an electrical discharge, as shown in U.S. Pat. No. 3,394,569 or when a hydraulic intensifier is used.
Thus, the need has existed for an apparatus for use in hydraulically bulge forming metal pulleys which mechanically locks the pulley forming dies in both the horizontal and vertical closed directions to prevent the formation of die junction marks on the formed pulley product.